animation example fixed


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1843 29e17f8d-cf37-471e-a288-72cc03a76eda
code moved to QwtSpline


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@1844 29e17f8d-cf37-471e-a288-72cc03a76eda